GB2425188A

GB2425188A - Fuel injection control

Info

Publication number: GB2425188A
Application number: GB0522066A
Authority: GB
Inventors: Jeffrey Allen
Original assignee: Scion Sprays Ltd
Current assignee: Scion Sprays Ltd
Priority date: 2005-10-28
Filing date: 2005-10-28
Publication date: 2006-10-18
Anticipated expiration: 2025-10-28
Also published as: GB2425188B; GB0522066D0

Abstract

With reference to Figure 6, the present invention provides an apparatus for controlling, within an internal combustion engine (600), a fuel injection period during which a fuel is injected into charge air to form a fuel/air mixture for combustion. The apparatus comprises: ```a pressure sensor (204) operable to detect a pressure of the charge air; ```a control unit (206) responsive to the pressure detected by the pressure sensor (204), the control unit being operable to detect a change in the pressure detected by the pressure sensor and to control the fuel injection period in dependence upon the time at which one or more of the detected pressure changes occurs; and ```a fuel injector (116) controlled by the controller. The pressure sensor(204), the control unit (206) and the fuel injector (116) are formed as a unitary fuel injection controller. The time at which the fuel injection period starts is controlled solely in dependence upon the time at which the pressure sensor (204) detects a pressure change. The system is cheap and simple, suitable for small engines such as used in engine-powered gardening tools.

Description

TIMING CONTROLLER

This invention relates to controlling, within an internal combustion engine, a combination interval during which a fuel and a gas are combined.

Most internal combustion engines in automobiles currently use fuel injection systems to supply fuel to the combustion chambers of the engine. Fuel injection systems have replaced the earlier technology of carburettors because they give better control of the delivery of fuel and enable the engine to meet emission legislation targets as well as improving overall efficiency.

It is important that the fuel injection system delivers an appropriate amount of fuel at an appropriate time.

Inappropriate delivery of the fuel may lead to a reduction in the output power of the engine and a wastage of fuel.

Therefore, to appropriately inject the fuel into the intake charge air, fuel injection systems make use of an engine control unit, an example of which is illustrated schematically in Figure 1 of the accompanying drawings.

Figure 1 illustrates a conventional internal combustion engine 100 comprising a cylinder 102 in which reciprocates a piston 104 with the piston 104 and the cylinder 102 defining between them a combustion chamber 106. The piston 104 is connected by a connecting rod 108 to a crankshaft 110. The crankshaft 110 drives a camshaft (not shown) which in turn drives an inlet valve 112 and an exhaust valve 114. The inlet valve 112 and the exhaust value 114 are driven in timed relationship to the movement of the piston 104 in the cylinder 102, with return springs (not shown) biasing the valves 112, 114 back into their valve seats.

The fuel injection system of the engine 100 comprises a fuel injector 116 arranged to deliver fuel 118 into an inlet passage 120 upstream of the inlet valve 112. A throttle valve 122 is placed in the inlet passage 120 to control the flow of charge air into the inlet passage 120 and the combustion chamber 106.

An engine control unit 124 controls the time at which the fuel 118 is injected into the charge air present in the inlet passage 120 and also controls the quantity of fuel 118 that is injected. The engine control unit 124 receives a signal from the throttle valve 122 via a control line 126, the signal indicating the rotational position of the throttle valve 122 and hence the engine load. Additionally, the engine control unit 124 receives a timing signal from a crankshaft sensor 128 (which could be replaced by a camshaft sensor) via a control line 130. The crankshaft sensor 128 is responsive to teeth 132 on the crankshaft 110 and to a gap 134 in the teeth 132. The engine control unit 124 can determine, from the timing signal received from the crankshaft sensor 128, the speed of the engine 100 and the position of the piston 104 within the cylinder 102, this being used to determine the timing of opening and closing of the inlet valve 112. Having regard to the timing signal produced by the crankshaft sensor 128 and the load signal produced by the sensor attached to the throttle valve 122, the engine control unit 124 generates a control signal which is relayed to the injector 116 via a line 136 and controls the operation of the injector 116.

Whilst the sophisticated and highly developed fuel injection systems currently available (as described above) are ideal for use in internal combustion engines in automobiles, there are many other applications for internal combustion engines where such a level of sophistication is not appropriate and too costly. For instance, small single cylinder engines as used for a variety of engine powered gardening devices (such as lawn mowers, hedge trimmers, chain saws, strimmers, rotovators, lawn aerators, scarifiers and shredders), small generators, mopeds, scooters, etc. are built to very tight cost targets and therefore cannot afford the cost of a sophisticated fuel injection system. To date, such small engines have used traditional cheaper carburettor technology. However, small engines of this type will soon face the same kind of exhaust gas emission legislation as automobile engines and so must be modified to meet the emission targets. Therefore, a cheap and simple system of fuel injection is required for such small engines.

According to a first aspect of the invention, there is provided an apparatus for controlling, within an internal combustion engine, a combination interval during which a fuel and a gas are combined, the apparatus comprising: a pressure sensor operable to detect a pressure of the gas; and a controller responsive to the pressure detected by the pressure sensor, the controller being operable to detect a change in the pressure detected by the pressure sensor and to control the combination interval in dependence upon the time at which one or more of the detected pressure changes occurs.

Internal combustion engines that make use of embodiments of the invention can do away with complicated, heavy and expensive fuel injection timing systems of the type that have been described above with reference to Figure 1. Instead, they may make use of a cheaper and simpler system that has a pressure sensor to detect the pressure of the intake charge air, with changes in the pressure then being detected and interpreted by a controller which uses this information to control the timing of the fuel injectors.

According to a second aspect of the invention, there is provided an internal combustion engine comprising an apparatus according to the first aspect of the invention.

According to a third aspect of the invention, there is provided an engine powered device comprising an internal combustion engine according to the second aspect of the invention.

The engine powered device may be an automobile.

Alternatively, the engine powered device may be a gardening device, such as a lawn mower, a hedge trimmer, a chain saw, a strimmer, a rotovator, a lawn aerator, a scarifier and a shredder.

According to a fourth aspect of the invention, there is provided a method for controlling, within an internal combustion engine, a combination interval during which a fuel and a gas are combined, the method comprising: a pressure detecting step for detecting a pressure of the gas; a change detecting step for detecting a change in the detected pressure of the gas; and a controlling step for controlling the combination interval in dependence upon the time at which one or more of the detected pressure changes occurs.

According to a fifth aspect of the invention, there is provided a computer program which, when executed by a computer, carries out a method according to the fourth aspect of the invention.

Further respective aspects and features of the invention are defined in the appended claims.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 schematically illustrates a conventional internal combustion engine; Figure 2 schematically illustrates an internal combustion engine having a fuel injection control system according to an embodiment of the invention; Figure 3A is a graph illustrating how the pressure of the air in an engine inlet passage changes when the engine is at full load; Figure 3B is a graph illustrating how the pressure of the air in an engine inlet passage changes when the engine is partially loaded; Figure 3C is a graph illustrating how the pressure of the air in an engine inlet passage changes when the engine is idle; Figure 4 schematically illustrates an engine control unit; Figure 5 is a schematic flowchart of the operation of the engine control unit illustrated in Figure 4; Figure 6 schematically illustrates an internal combustion engine having a fuel injection control system according to a second embodiment of the invention; and Figure 7 schematically illustrates an internal combustion engine having a fuel injection control system according to a further embodiment of the invention.

Figure 2 schematically illustrates an internal combustion engine 200 having a fuel injection control system according to an embodiment of the invention. The internal combustion engine 200 is similar to the internal combustion engine 100 shown in Figure 1. Components of the engine 200 that are the same as components of the engine 100 are given the same reference numeral and, for clarity, a description of them will not be repeated.

The engine 200 has a crankshaft 202, which is similar to the crankshaft 110 shown in Figure 1, except that the crankshaft 202 does not have the teeth 132 and hence does not have the gap 134.

The engine 200 also has a pressure sensor 204 for detecting the pressure of the air within the inlet passage 120. The pressure sensor 204 supplies an engine control unit 206 with a pressure signal via a control line 208.

The engine control unit 206 determines, from the pressure signal received from the pressure sensor 204: (i) the engine load; (ii) the engine speed; and (iii) the timing of the opening and/or closing of the inlet valve 112.

This will be described in more detail later. In addition, as before, the engine control unit 206 generates a control signal which is relayed to the injector 116 via the line 136 and controls operation of the injector 116.

In the engine 100 shown in Figure 1, the engine control unit 124 uses the signal from the crankshaft sensor 128 to determine the engine speed and the timing of the opening and closing of the inlet valve 112. Therefore, it will be appreciated that, as the engine control unit 206 determines both the engine speed and the timing of the opening and closing of the inlet valve 112 from the pressure signal received from the pressure sensor 204, the engine 200 does not require the crankshaft sensor 128 of the engine 100 (nor the control line 130) . This is the reason that the crankshaft 202 of the engine 200 is more simply formed than the crankshaft 110 of the engine 100, i.e. the crankshaft 200 does not need to be provided with the teeth 132 and the gap 134, these being provided to the crankshaft 110 to enable the crankshaft sensor 128 to perform its task.

Furthermore, in the engine 100 shown in Figure 1, the engine control unit 128 uses the load signal from the sensor attached to the throttle valve 122 to determine the engine load. Therefore, it will be appreciated that, as the engine control unit 206 determines the engine load from the pressure signal received from the pressure sensor 204, the engine 200 does not require the sensor attached to the throttle valve (nor the control line 126).

Figure 3A is a graph illustrating how the pressure 300 of the air in the inlet passage 120, as detected by the pressure sensor 204, changes as the piston 104 cycles between the top-dead-centre (TDC) position within the cylinder 102 (at which the piston 104 is furthest from the crankshaft 202) and the bottom-dead-centre (BDC) position within the cylinder 102 (at which the piston 104 is closest to the crankshaft 202) . As a reference pressure, atmospheric pressure 302 is represented by a horizontal straight line on the graph. The average detected pressure 303 over an engine cycle is represented by a horizontal dashed line on the graph, the difference between atmospheric pressure 302 and the average detected pressure 303 being d.

As can be seen, there are sharp peaks 304 in the pressure detected by the pressure sensor 204. Each of the sharp peaks 304 corresponds to the closing of the inlet valve 112 during the engine cycle. Closing the inlet valve 112 causes a "pressure pulse" within the inlet passage 120.

This pressure pulse corresponds to the sharp increase of the peak 304. However, this pressure pulse effect soon dies away and the pressure of the air within the inlet passage 120 returns to approximately atmospheric pressure 302. This corresponds to the sharp decrease of the peak 304.

Additionally, there is another peak 306 in the pressure detected by the pressure sensor 204. This peak 306 results from the opening of the inlet valve 112. The arrangement of the crankshaft 202 and the camshaft causes the inlet valve 112 to open as the piston 104 is still rising within the cylinder 102. The peak 306 results from the exhaust gas in the cylinder 102 being forced into the inlet passage 120 by the higher pressure during the exhaust stroke.

As the piston 104 then moves down within cylinder 102 and draws in the air and fuel mixture into the cylinder 102, the movement of the air in the inlet passage 120 causes a drop in the pressure of the air within the inlet passage 120.

Figure 3A is a graph for when the engine 200 is at full load. Figures 3B and 3C are similar to the graph of Figure 3A, except that the graph of Figure 3B is for when the engine 200 is partially loaded and the graph of Figure 3C is for when the engine 200 is idle. As can be seen, the pressure changes detected by the pressure sensor 204 during an engine cycle are dependent upon the engine load. In particular, when the engine 200 is fully loaded, the throttle valve 122 is fully open, meaning that the pressure of the air in the inlet passage 120 can quickly return to atmospheric pressure 302 following the closure of the inlet valve 112. However, when the engine 200 is idle (or partially loaded), the throttle valve 122 reduces the rate at which air can enter and leave the inlet passage 120, resulting in a slower return of the pressure of the air within the inlet passage 120 to atmospheric pressure 302.

This results in a larger difference d at lower engine loads. However, the peaks 304 and 306 occurring in response to the closure and opening of the inlet valve 112 are still clearly discernable in each of the graphs of Figures 3A-C.

Figure 4 schematically illustrates the engine control unit 206. The pressure signal from the pressure sensor 204 representing the pressure of the air in the inlet passage is received by the engine control unit 206 via the control line 208. The pressure signal is then supplied to a low pass filter unit 400 and a high pass filter unit 402.

The outputs of the low pass filter unit 400 and the high pass filter unit 402 are supplied to a processor unit 404.

The processor unit 404 has access to a look-up-table 406 stored in a memory 408. The processor unit 404 uses the output of the low pass filter unit 402, the output of the high pass filter unit 404 and the look-uptable 406 to generate a control signal to be supplied to the injector 116 via the control line 136.

As will be described, the processor unit 404 uses the low pass filtered pressure signal to determine the load of the engine 200. The processor unit 404 also uses the high pass filtered pressure signal to determine the speed of the engine 200 and the timing of the opening and closing of the inlet valve 112.

Figure 5 is a schematic flowchart of the operation of the engine control unit 206 illustrated in Figure 4.

At a step S500, the engine control unit 206 receives the pressure signal from the pressure sensor 204, the - 10 - pressure signal representing the pressure of the air within the inlet passage 120.

At a step S502, the low pass filter unit 400 low pass filters the input pressure signal and outputs a low pass filtered pressure signal to the processor unit 404.

At a step S504, the high pass filter unit 402 high pass filters the input pressure signal and outputs a high pass filtered pressure signal to the processor unit 404.

At a step S506, the processor unit 404 uses the high pass filtered pressure signal output by the high pass filter unit 402 to determine the timing of the peaks 304 in the pressure signal received from the pressure sensor 204. This may be performed in any conventional manner, such as detecting the occurrence of a peak 304 when the magnitude of the high pass filtered pressure signal exceeds a threshold value. It will be appreciated, therefore, that the particular high pass filter used by the high pass filter unit 400 is preferably such that the peaks 304 can be easily identified.

The time between successive peaks 304 that represent the closing of the inlet valve 112 is directly related to the speed of the engine 200: namely, the inlet valve 112 opens and closes once for every two revolutions of the crankshaft 202 (i.e. for one engine cycle) . The processor unit 404 therefore calculates the engine speed from the time between successive peaks 304 that represent closing the inlet valve 112 (or the time between successive peaks 306 that represent opening the inlet valve 112). It is preferred to use peaks 304 since they are higher and sharper than peaks 306 and therefore give the clearest signal for engine speed and timing reference. However, the peaks 306 could be alternatively or additionally used.

- 11 - Next, at a step S508, the load of the engine is determined from the detected pressure. The processor unit 404 determines the average detected pressure 303 over an entire engine cycle (such as between successive closures of the inlet valve 112) . The processor unit 404 uses the low pass filtered pressure signal from the low pass filter unit 402 to determine the average detected pressure 303 so that the effects of the peaks 304 and 306 in the detected pressure are minimized. The difference d between the average detected pressure 303 and atmospheric pressure 302 is used as an indicator of the engine load. The smaller the value of this pressure difference d, the higher the engine load.

At a step S5l0, the processor unit 404 references the look-up-table 406 to determine how to control the duration of a combination interval for combining the fuel 118 with the air in the inlet passage 120. The look-uptable 406 will be described in more detail later.

At a step S512, the processor unit 404 determines when fuel injection should begin for the current engine cycle, i.e. the start of the combination interval for the current engine cycle. In particular, the combination interval will start at a predetermined time relative to the opening of the inlet valve 112. The processor unit 404 estimates when the inlet valve will open in the current engine cycle based on the time during the previous engine cycle at which the inlet valve 112 opened. For example, the processor unit calculates the time between the closing of the inlet valve 112 and the opening of the inlet valve 112 in the previous engine cycle and assumes that this time period will be the same for the current engine cycle. When the processor unit 404 detects the closure of the inlet valve 112 for the - 12 - current engine cycle, it can then simply work out when the inlet valve 112 is expected to open next. Alternatively, for an engine designed to run at a constant engine speed, the processor unit 404 simply needs to know the time during the previous engine cycle at which the inlet valve 112 opened, from which it can then calculate the time at which the inlet valve 112 is expected to open during the current engine cycle.

Finally, at a step S514, the processor unit 404 generates an appropriate control signal for the injector 116 and outputs the control signal on the line 136.

The look-up-table 406 stores, for a given range of engine loads and a given range of engine speeds, a corresponding indication of the amount of fuel 118 that is to be injected into the air in the inlet passage 120. Note that the range of engine speeds may be represented by a range of the time between successive peaks 304 (or 306) in the detected pressure.

The indications of the amount of fuel are indications of the length of time (pulse width) that the fuel injector 116 should be activated for, given the specified engine speed and load. Alternatively, the indication may be a number of discrete injections of a fixed quantity of the fuel 118. In either case, the length of the combination interval during which the fuel 118 and the air are combined is defined in the look-up-table 406 (either by the pulse width of a single fuel injection or by the number of discrete injections of a fixed fuel quantity) . This then defines the amount of fuel 118 to be combined with the air in the inlet passage 120 during the current engine cycle.

It will be appreciated that the engine control unit 206 may store a computer program which the processor unit 404 - 13 - executes in order to perform the timing control of the injector 116. The computer program may be stored together with the look-up-table 406 in the memory 408.

The engine control unit 206 may store a reference value for atmospheric pressure 302, 50 that it can calculate the pressure difference d. Alternatively, the engine control unit may receive an input from another pressure sensor (not shown) that detects the current value of atmospheric pressure 302. This pressure sensor could be the pressure sensor 204, with atmospheric pressure 302 being detected prior to starting the engine 200.

It will be appreciated that the engine control unit 206 need not make use of a low pass filter unit 400 to determine the average pressure 303. For example, the processor 404 could simply average the pressure signal received directly from the pressure sensor 204 over an engine cycle.

Furthermore, the engine control unit 206 need not make use of a high pass filter unit 402 to determine the peaks 304 and 306 in the pressure detected by the pressure sensor 204. For example, the processor 404 could simply search for local maxima in the pressure signal received directly from the pressure sensor 204. Additionally, the processor 404 could perform standard signal processing techniques to determine the periodicity of the pressure signal received directly from the pressure sensor 204.

Figure 6 schematically illustrates an internal combustion engine 600 having a fuel injection control system according to another embodiment of the invention. The engine 600 of Figure 6 is similar to the engine 200 of Figure 2, except that the fuel injector 116, the pressure sensor 204 and the engine control unit 206 are formed as a unitary fuel injection controller 602.

- 14 - It will be appreciated that the engine control unit 206 of the engine 200 of Figure 2 and the engine 600 of Figure 6 could be arranged so as to not estimate the engine load (and therefore not have the low pass filter unit 400) . In this case, the engine control unit 206 receives an input signal indicative of the engine load from an alternative source (for example, from a sensor on the throttle valve 122 via the control line 126, as in Figure 1) Such an alternative embodiment is illustrated schematically in Figure 7, which illustrates an internal combustion engine 700 having a fuel injection control system similar to that of the engine 600 of Figure 6. The engine 700 has a unitary fuel injection controller 702 that is the same as the unitary fuel injection controller 602 of the engine 600, except that it comprises a potentiometer 704 coupled to the throttle valve 122. The potentiometer 704 provides a control signal, indicative of the rotational position of the throttle valve and hence indicative of the engine load, to the engine control unit 206 via a control line 706. The engine control unit 206 also receives the detected pressure signal from the pressure sensor 204 and uses this (as described above) to determine the speed of the engine 700 and the timing of the opening and closing of the inlet valve 112. The engine control unit 206 then controls the injector 116 in the same way as has been described above.

It will be appreciated that, in an internal combustion engine having more than one cylinder 102, a pressure sensor 204 may be provided at the inlet passage 120 of each of the cylinders 102, with a single engine control unit 206 receiving a pressure signal from each of the pressure sensors 204 and outputting a control signal to the - 15 - corresponding injectors 116 as appropriate using per- cylinder based timing calculations.

Alternatively, in an internal combustion engine having more than one cylinder 102, a single pressure sensor 204 may be provided to detect pressure changes from more than one of the cylinders 102. The engine control unit 206 then detects the opening and closing of multiple inlet valves 112. In the case in which a single injector 116 is used for all of the cylinders 102, then the engine control unit 206 controls the injector 116 in a manner similar to that which has been described above, except that during one complete engine cycle, the injector 116 will be activated for more than one combination interval. In the case in which each cylinder 102 has its own injector 116, then the engine control unit needs to know which of the multiple inlet valves 112 is opening and closing so that it can control the corresponding injector 116 at the appropriate time. The engine control unit 206 can determine this if the timing order for opening and/or closing the inlet valves 112 is arranged to have a distinctive timing characteristic that is detectable from the pressure signal generated by the pressure sensor 204 and received by the engine control unit 206.

It is often the case that an internal combustion engine is only run at a constant speed but with a varying load.

Examples of this include internal combustion engines used in gardening equipment (such as lawn mowers, rotovators, hedge trimmers, strimmers, chain saws, lawn aerators, scarifiers, shredders, etc.). As such, the look-up-table 406 can be simplified such that it stores, for a given range of engine loads (but not engine speeds), an indication of the amount of the fuel 118 that is to be injected into the air in the inlet passage 120. As has been described above, this - 16 - indication may be the length of time (pulse width) that the fuel injector 116 should be activated for, given the specified engine load. Alternatively, the indication may be a number of discrete injections of a fixed quantity of the fuel 118. In either case, the length of the combination interval during which the fuel 118 and the air are combined is defined, either by the pulse width of a single fuel injection or by the number of discrete injections of a fixed fuel quantity.

The gas present in the inlet passage 120 will, in many internal combustion engines, be air. However, it will be appreciated that a gas other than air may be used within the internal combustion engine for combination with the fuel 116. Any gas which, when combined with the fuel 116, is suitable for combustion within the combustion chamber 106 may be used.

Claims

- 17 - CLAI MS

1. An apparatus for controlling, within an internal combustion engine, a combination interval during which a fuel and a gas are combined, the apparatus comprising: a pressure sensor operable to detect a pressure of the gas; and a controller responsive to the pressure detected by the pressure sensor, the controller being operable to detect a change in the pressure detected by the pressure sensor and to control the combination interval in dependence upon the time at which one or more of the detected pressure changes occurs.

2. An apparatus according to claim 1, in which the controller controls the time at which the combination interval starts in dependence upon the time at which a detected pressure change occurs.

3. An apparatus according to any one of the preceding claims, in which the controller controls the duration of the combination interval in dependence upon the time between the occurrence of two detected pressure changes.

4. An apparatus according to any one of the preceding claims, in which the controller comprises a high pass filter unit operable to high pass filter a pressure signal representing the pressure detected by the pressure sensor, the controller detecting a change in the detected pressure in dependence on the high pass filtered pressure signal.

- 18 -

5. An apparatus according to any one of the preceding claims, in which the controller comprises a load determination unit operable to determine a load on the engine, the controller being operable to control the duration of the combination interval in dependence on the load on the engine determined by the load determination unit.

6. An apparatus according to claim 5, in which the load determination unit is responsive to the pressure detected by the pressure sensor.

7. An apparatus according to claim 6, in which the load determination unit is operable to determine an average value of a pressure signal representing the pressure detected by the pressure sensor and to determine the load on the engine in dependence on a difference between the determined average value and a reference pressure.

8. An apparatus according to claim 7, in which the load determination unit comprises a low pass filter unit operable to low pass filter the pressure signal, the load determination unit determining the average value in dependence on the low pass filtered pressure signal.

9. An apparatus according to claim 5, in which the load determination unit is operable to receive a load signal indicating an amount of the gas available for the combination of the gas and the fuel and to determine the load on the engine in dependence on the received load signal.

- 19 -

10. An apparatus according to claim 9, in which the load signal indicates a position of a throttle valve of the engine.

11. An apparatus according to any one of claims 5 to 10, in which the controller stores a table having information indicating a duration of the combination interval for each of one or more ranges for the load on the engine, the controller using the table to control the duration of the combination interval.

12. An apparatus according to claim 11, when dependent on claim 3, in which the table has information indicating a duration of the combination interval for each of one or more pairs of a range for the load on the engine and a range for the time between the occurrence of two detected pressure changes.

13. An apparatus according to any one of the preceding claims, in which the apparatus comprises a combiner controlled by the controller and operable to combine the fuel and the gas during the combination interval determined by the controller.

14. An apparatus according to any one of the preceding claims, in which the combination interval is an interval during which the fuel is to be continuously combined with the gas.

15. An apparatus according to any one of claims 1 to 13, in which the combination interval is an interval having one or - 20 - more combination times at each of which a predetermined quantity of the fuel is to be combined with the gas.

16. An apparatus for controlling, within an internal combustion engine, a combination interval during which a fuel and a gas are combined, the apparatus being substantially as hereinbefore described with reference to Figures 2 to 7 of the accompanying drawings.

17. An internal combustion engine comprising an apparatus according to any one of the preceding claims.

18. An internal combustion engine substantially as hereinbefore described with reference to Figures 2 to 7 of the accompanying drawings.

19. An engine powered device comprising an internal combustion engine according to claim 17 or 18.

20. A device according to claim 19, in which the device is an engine driven vehicle.

20. A device according to claim 19, in which the device is a gardening device.

21. A device according to claim 20, in which the device is selected from the list comprising: a lawn mower; a hedge trimmer; a chain saw; a strimmer; a rotovator; a lawn aerator; a scarifier; and a shredder.

- 21 - 22. A device according to claim 19, in which the device is an engine driven vehicle.

23. A method for controlling, within an internal combustion engine, a combination interval during which a fuel and a gas are combined, the method comprising: a pressure detecting step for detecting a pressure of the gas; a change detecting step for detecting a change in the detected pressure of the gas; and a controlling step for controlling the combination interval in dependence upon the time at which one or more of the detected pressure changes occurs.

24. A method according to claim 23, in which the controlling step controls the time at which the combination interval starts in dependence upon the time at which a detected pressure change occurs.

25. A method according to any one of claims 23 to 24, in which the controlling step controls the duration of the combination interval in dependence upon the time between the occurrence of two detected pressure changes.

26. A method according to any one of claims 23 to 25, in which the change detecting step comprises high pass filtering a pressure signal representing the detected pressure of the gas and detecting a change in the detected pressure of the gas in dependence upon the high pass filtered pressure signal.

- 22 - 27. A method according to any one of claims 23 to 26, in which the controlling step comprises a load determining step for determining a load on the engine, the combination interval being controlled in dependence on the load on the engine determined at the load determining step.

28. A method according to claim 27, in which the load on the engine is determined in dependence on the detected pressure of the gas.

29. A method according to claim 28, in which the load on the engine is determined in dependence on a difference between an average value of the detected pressure of the gas and a reference pressure.

30. A method according to claim 29, in which the load determining step comprises low pass filtering a pressure signal representing the detected pressure of the gas, the average value of the detected pressure of the gas being determined in dependence on the low pass filtered pressure signal.

31. A method substantially as hereinbefore described with reference to Figures 2 to 7 of the accompanying drawings.

32. A computer program which, when executed by a computer, carries out a method according to any one of claims 23 to 31.

Amendments to the claims have been filed as follows

CLAI MS

1. An apparatus for controlling, within an internal combustion engine, a fuel injection period during which a fuel is injected into charge air to form a fuel/air mixture for combustion, the apparatus comprising: a pressure sensor operable to detect a pressure of the charge air; a control unit responsive to the pressure detected by the pressure sensor, the control unit being operable to detect a change in the pressure detected by the pressure sensor and to control the fuel injection period in dependence upon the time at which one or more of the detected pressure changes occurs; and a fuel injector controlled by the control unit; wherein: the pressure sensor, the control unit and the fuel injector re formed as a unitary fuel injection controller; and he time at which the fuel injection period starts is controlled solely in dependence upon the time at which the pressure sensor detects a pressure change.

2. An apparatus according to claim 1, in which the control unit controls the duration of the fuel injection period in dependence upon the time between the occurrence of two detected pressure changes.

3. An apparatus according to claim 1 or claim 2, in which the control unit comprises a high pass filter unit operable to high pass filter a pressure signal representing the pressure detected by the pressure sensor, the controller: -2k- detecting a change in the detected pressure in dependence on the high pass filtered pressure signal.

4. An apparatus according to any one of the preceding S claims, in which the unitary fuel injection controller comprises a load determination unit operable to determine a load on the engine, the controller being operable to control the duration of the fuel injection period in dependence on the load on the engine determined by the load determination unit.

5. An apparatus according to claim 4, in which the load determination unit is responsive to the pressure detected by the pressure sensor.

6. An apparatus according to claim 5, in which the load determination unit is operable to determine an average value of a pressure signal representing the pressure detected by the pressure sensor and to determine the load on the engine in dependence on a difference between the determined average value and a reference pressure.

7. An apparatus according to claim 6, in which the load determination unit comprises a low pass filter unit operable to low pass filter the pressure signal, the load determination unit determining the average value in dependence on the low pass filtered pressure signal.

8. An apparatus according to claim 4, in which the load determination unit is operable to receive a load signal indicating an amount of the charge air and to determine the Thc- load on the engine in dependence on the received load signal.

9. An apparatus according to claim 8, in which the load signal indicates a position of a throttle valve of the engine.

10. An apparatus according to any one of claims 4 to 9, in which the control unit stores a table having information indicating a duration of the fuel injection period for each of one or more ranges for the load on the engine, the control unit using the table to control the duration of the combination interval.

11. An apparatus according to claim 10, when dependent on claim 2, in which the table has information indicating a duration of the fuel injection period for each of one or more pairs of a range for the load on the engine and a range for the time between the occurrence of two detected pressure changes.

12. An apparatus according to any one of the preceding claims, in which the fuel injection period is a period during which the fuel is to be continuously injected into the charge air.

13. An apparatus according to any one of claims 1 to 11, in which the fuel injection period is a period having one or more injection pulses in each of which a predetermined quantity of the fuel is to be combined with the charge air.

14. An apparatus for controlling, within an internal combustion engine, an injection period during which a fuel is injected into air to form a fuel/air mixture for combustion, the apparatus being substantially as hereinbefore described with reference to Figures 6 and 7 of the accompanying drawings.

15. An internal combustion engine comprising an apparatus according to any one of the preceding claims.

16. An internal combustion engine substantially as hereinbefore described with reference to Figures 6 and 7 of the accompanying drawings.

17. An engine powered device comprising an internal combustion engine according to claim 15 or 16.

18. A device according to claim 17, in which the device is a gardening device.

19. A device according to claim 20, in which the device is selected from the list comprising: a lawn mower; a hedge trimmer; a chain saw; a rotovator; a lawn aerator; a scarifier; and a shredder.